The present invention relates to systems for displaying video images and methods for reducing and filtering the video images.
Modern-day television sets offer many options for the viewer. One option is known as the xe2x80x9cpicture-in-picturexe2x80x9d or xe2x80x9cPIPxe2x80x9d feature in which a reduced-size video image for one channel is overlaid on a fall-size video image for another channel.
To shrink a video image from full-size to reduced-size, the hardware typically removes some of the video data. For example, a video input stream for fall-size images might comprise pixel data for a 640xc3x97480 pixel display, whereas the reduced size images might only require data for a 160xc3x97120 area. Elimination of data often results in noticeable differences between pixels in a scan line, or between one scan line and the next. Smooth transition between pixels is lost and the overall image appears to xe2x80x9cflickerxe2x80x9d. The xe2x80x9cflickerxe2x80x9d artifact is particularly noticeable in the situation where a horizontal scan line differs noticeably from neighboring scan lines above and below.
One solution is to use simple graphics hardware or optimized software to perform drop sampling on the large image, discarding pixels to create the smaller image. Unfortunately, this solution introduces a significant amount of aliasing, which is particularly noticeable in video with a large degree of motion. The aliasing also introduces interlace flickering.
Another solution is to employ complex graphics hardware to perform de-interlacing and multi-tap filtering on the video stream at real-time rates. This solution requires significant memory bandwidth to read pixels multiple times for use in the filtering process. Unfortunately, this solution comes with a high price tag.
Accordingly, there is a need for a technique that reduces image size while minimizing aliasing and removing interlace flicker, yet can be implemented using simple graphics hardware or optimized software.
This invention concerns systems and methods for resizing and filtering a video data stream to produce a reduced-size display image while minimizing aliasing and removing interlace flicker. The techniques may be implemented using simple graphics hardware or optimized software.
In one implementation, a system for processing a video data stream has a data input to receive the video data stream. The video data stream has odd and even fields of interlaced scan lines. The system also has a resizing and filtering component that processes video data stream to reduce the size of the image when displayed and to remove interlace flickering.
The resizing and filtering component initially removes the odd (or even) field of interlaced scan lines, thereby reducing the quantity of video data by one-half. The resizing and filtering component then resizes and filters the remaining second field of interlaced scan lines as follows:
(Lineindex+1xe2x88x92ratio)/4+(Lineindex+Lineindex+1)/4+(Lineindex+ratio)/4
wherein xe2x80x9cLinexe2x80x9d is a scan line, xe2x80x9cRatioxe2x80x9d is an amount of scaling to be performed, and xe2x80x9cIndexxe2x80x9d is a scan line number that starts at zero and increments in steps of the xe2x80x9cRatioxe2x80x9d.
For a case involving six sequential odd (or even) scan lines A-F and a reduction factor of 2:1, the above resize and filter process reduces to:
(B+C+D+E)/4.
For a case involving six sequential odd (or even) scan lines A-F and a reduction factor of 3:2, the above resize and filter process reduces to:
B/2+C/4+D/4 and C/4+D/4+E/2.
The resizing and filtering component is beneficial in that it requires few input samples (e.g., only four input pixels for each output pixel) in comparison to a fall, multi-tap filter. As a result, the component can be implemented in software or simple hardware with few shift and add operations. Yet, the low cost component still effectively reduces the flicker artifact in the reduced-size image.